The present invention concerns means to guide the to-and-fro motion of a pair of weft carrying grippers inside the shed of looms with continuous weft feed, of the type comprising two control straps movable in a substantially horizontal plane thanks to the action of two gearwheels with reciprocating motion, and a plurality of guide elements for the straps, aligned on the sley facing the reed and positioned perpendicularly thereto.
It is known that modern shuttleless looms, of the type specified heretofore, still have no solve the problem of efficiently guiding the weft carrying grippers inside the shed, to guarantee that the reciprocal movements of said grippers, as well as their motion in respect of the sley and of the reed, are correct and, at the same time, to limit as far as possible the wear on the grippers, on the straps and on the other members involved in their motion, and the stresses on the warp yarns through which weft insertion is carried out.
In spite of the great number of improvements introduced in said guide means, especially in recent years, the attempts made up to date to satisfactorily meet the different and contrasting requirements of this essential aspect of the planning and construction of weaving machines, have proved unsuccessful.
A brief outline of the solutions so far adopted may help to explain the situation.
In the first shuttleless weaving looms, the motion of the grippers was guided (and it has been so far many years, and it is still so in many types of looms) by means of two parallel and close rows of elements guiding the gripper straps on both sides, respectively on the side of the reed and on the side of the fabric being formed. These elements, mounted on the sley, were in the form of opposed hooks, having substantially rectangular seats into which the straps engaged to slide with their lateral surfaces and with the ends of their upper and lower surfaces.
This arrangement soon showed its weaknesses, since the substantially correct guiding of the grippers was accompanied by:--excessive wear of the straps, determined by the particlar location and very limited extension of the area of the friction surfaces, grown soon intolerable as loom speeds were increasing;--damaging or breakage of weft yarns inserting themselves, due for instance to insufficient tension and/or to having been lowered by the upper warp years, into the seat for the strap of the guide elements of the row close to the reed, and getting caught by said elements;--and, above all, unacceptable damaging of the warp yarns subject to being: undesirably spread apart by the elements guiding the row close to the reed; easily caught (when deviated from their natural positioning in planes perpendicular to the sley) into the seats for the strap, by the guide elements of the same row, with evident risk of breakage; easily caught ("pinched"), and thus cut or seriously damaged, between the strap and the seats therefor of opposite guide elements (when loosening in proximity to pairs of said elements).
The efforts of designers have been directed to overcoming all the above drawbacks in the means guiding the motion of weft carrying grippers inside the shed of looms, gut so far, they have led only to very partial solutions ofthe problems involved.
The most interesting attempts include those made by the Applicant with the solutions provided by the European patent applications No. 84111236.0 and No. 86107378.1. In the first case, the improvement concerned the shape of the seats of the hook elements guiding the strap (for the remaining part of conventional type), in order to eliminate or reduce the risk of the warp yarns close to said elements getting caught between the seats therefor and the strap. In the second case, the improvement was to eliminate the row of guide elements close to the reed, and to leave the function of engaging and efficiently guiding both the straps and the grippers to the only remaining row of hook guide elements, suitably adapted as to shape and structure.
These arrangements, though providing an efficient solution to the specific problems faced, did not however allow overcoming the remaining drawbacks, whereby they turned out to be almost useless. In particular, the second solution did not solve the problems for which the first solution had been conceived, and viceversa. Furthermore, none of the two cited improved arrangements faced the problems of wear, which remained particularly serious in the case of the second solution, plaqued also by problems of strap hunting downstream of the gripper, while the first solution did not improve at all the drawbacks connected with irregular loose and/or lowered wefts.
Also another solution of known technique--that of the Swiss Patent No. 589.736, consisting in limiting the guide elments to a single row of elementary hooks facing the reed, to guide the gripper carrying straps only on their edge towards the fabric, on the side and from the top, letting them instead free ot slide at the bottom, on the lower warp lap, and on the other side against the reed--had not given satisfactory results, both because, especially at high speeds, the guiding of the strap and thus of the grippers was insufficiently precise (even if it eliminated the problems connected with the spreading apart of warp yarns and the catching of warp and weft yarns by the guide elements of the row - which had been abolished--close to the reed, and those connected with the "pinching" of the yarns of the lower warp lap, on which the strap was simply bearing along its path), and because it also required an operation of reed shimming and the use of special (semirigid) straps apt to keep their trajectory constant, which involved high costs.